homologous_recombination

homologous_recombination - BIOC2603 Principles of Molecular...

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BIOC2603 Principles of Molecular Genetics Recombination Brian Wong bcwwong@hkucc.hku.hk
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Genetic recombination: reassortment of genetic material (A) Independent assortment (for genes on different chromosomes) (B) crossing over (for genes on the same chromosome) Crossover is the breakage of the two DNA molecules at the same position and their rejoining in two reciprocal recombinations.
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Independent assortment produces 50 percent recombinants
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For linked genes, recombinant frequencies are less than 50 percent
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Four types of recombination 1. Homologous recombination (general recombination) Requires extensive sequence similarity between the two recombining DNA Takes place anywhere along the DNA 2. Site-specific recombination Occurs between two very limited and specific DNA sequences on both of the recombining DNA The two parental recombination sites are conserved in a simple reciprocal recombination event XX AB b a AC c a C c b B X CD DC
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Four types of recombination 3. Transposition Involves interaction of the two ends of a transposable element with a random site on the same or another DNA molecule Results in a new position and/or proliferation of the transposable element 4. Illegitimate recombination Processes that require neither sequence homology or site specificity e.g. non-homologous end joining +
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Biological roles of recombination • To generate genetic diversity • For repair and replication • To control gene expression (genetic switches) • Genome evolution • Introduces mutations and may result in diseases
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Part I Homologous Recombination
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Homologous recombination involves breakage and reunion of genetic material • recombination by breakage and rejoining: involve the physical exchange of genetic material between the two recombining DNA • recombination by copy choice: recombination occurs during replication by copying partly from one parent and partly from the other X AB b a A a b B b a b A
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h cI h + cI + 15 N, 13 C labeled (Heavy) 15 N, 13 C labeled (Heavy) λ phage 1 λ phage 2 Infect bacteria in 14 N, 12 C (light) medium. Separate phage progenies based on the densities of DNA by using CsCl density centrifugation. h cI + h + cI X “Heavy” recombinants were identified – consistent with the breakage and reunion hypothesis. The copy-choice hypothesis predicted all recombinants were labled with 14 N and 12 C (light). + Homologous recombination involves breakage and reunion of genetic material Meselson M (1964) J. Mol. Biol. 9:734-745.
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C, colored; c, colorless Wx, waxy; wx, starchy knob extra piece of DNA Recombinants Recombination between C / c and Wx / wx Corn with unusual chromosome Cytological crossing-over accompanied by genetical crossing-over Homologous recombination involves breakage and reunion of genetic material
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Grow cells in the presence of BrdU .
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This note was uploaded on 03/19/2010 for the course BIOC BIOC2603 taught by Professor Dr.mhsham during the Spring '07 term at HKU.

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homologous_recombination - BIOC2603 Principles of Molecular...

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